1. Field of the Invention
The present invention relates to industrial sealing parts which are used in those such as car vehicles, electric instruments, machine tools or the like. More particularly, the present invention relates to sealing devices for establishing a seal between relatively movable shaft and housing. More particularly, the present invention relates to sealing devices with a harder portion on an inner surface of a sealing lip, to provide said sealing lip with hydrodynamic pumping effects to pump back oil or fluid to be sealed to the oil or fluid side.
The present invention also relates to a process to make a sealing device having a sealing lip comprising harder helical or circular or screw portions on the inner surface of the sealing lip, the hardened portions are made by irradiation of radiation ray.
2. Description of the Related Art
Conventionally, a sealing device of this type, for example, as is shown in FIG. 10 has been used so far. FIG. 10 is a fragmentary cross-sectional view showing a conventional sealing device which is mounted on a shaft.
As shown in FIG. 10, the sealing device is used to seal a distance or a gap between a housing 500 and a shaft 600, preventing a fluid (oil or the like) to be sealed from leaking from a fluid (oil or the like) side O to an air-side A.
The sealing device 400 has a rigid (metal) annular casing 401 with a sealing member such as a sealing lip (402, 405) which is formed on the rigid annular casing 401 in one body. A radially inwardly tip portion of an inner periphery of the sealing lip is urged toward the shaft 600 to make the tip portion slidably and sealingly engage with the shaft 600, by a garter spring 403 in a spring holder 404 (as shown in FIG. 10).
A secondary sealing lip (dust sealing lip) 405 in FIG. 10 is additionally formed in the air-side A of the sealing device for preventing contaminants from entering into the oil-side O from the air-side A.
In such a conventional sealing device 400, in order to secure more effective sealing properties, the main sealing lip 402 has an important element, such as a helical pumping rib 406 (as shown in FIGS. 11 and 12) on the inner surface of the sealing lip.
FIG. 11 is a fragmentary cross-sectional view showing a conventional sealing device, and FIG. 12 is a cross-sectional view taken along the line Y-Yxe2x80x2. As shown in FIG. 11, on the inner surface of the main sealing lip 402 a plurality of helical pumping ribs 406 are formed. By providing these helical pumping ribs, pumping functions to pump back fluid or oil to be sealed to the oil-side O is effectively secured.
Conventional sealing device mentioned above has following shortages.
1. In order to provide such helical pumping ribs on the inner surface of the sealing lip, sealing devices are transfer or injection molded in a mold having helical pumping ribs thereof. To provide helical pumping ribs in the mold, however, causes shortages such as an increase of a burden in designing or processing, to cause increase in cost.
2. On the other hand, in the case that these convexo-concave portions 406 of helical pumping ribs are provided on the inner surface of the sealing lip, the convex portions tend to be exposed to a severe friction with the shaft 600 compared with portions other than the convex portions of the inner surface of the sealing lip, causing severe abrasion especially at the convex portions to bring the initial configuration (shape) of the helical ribs into other configuration (shape) with proceeding of abrasion. These phenomena cause unstable sealing properties of conventional sealing devices in long use.
To cope with these problems mentioned above, it is necessary for us, by estimating the change of the configuration (shape) of the helical ribs with proceeding of the abrasion at the portion of the ribs, to design the shape of the helical ribs precisely, so that the sealing devices have stable sealing properties even in the long use. It is, however, very difficult to estimate accurate abrasion mode, as well as to design the shape of the ribs based on the estimated abrasion mode in long use.
Another type of conventional sealing device is shown in FIG. 13. As is shown in FIG. 13, another type of conventional sealing device 700 is designed to seal a distance or a gap between an annular housing 900 and a shaft 800, preventing a fluid (oil or the like) to be sealed from leaking from a fluid (oil or the like) side O to an air-side A.
The conventional sealing device 700 has a rigid (metal) annular casing 701 with a rubber sealing member 702 in one body, and with a resin sealing member 703 which is placed between and held by the annular rigid casing 701 and the rubber sealing member 702. The rubber sealing member 702 comprises a radially outer peripheral sealing portion 702b which firmly contacts with the housing to seal a fluid, a sealing lip 702a which slides on the seals the shaft 800, and a radially extending portion 702c which connects to the radially outer peripheral sealing portion 702b, in one body.
The resin sealing member 703 backs up a base portion 702d of the sealing lip 702a of the rubber sealing member 702 to prevent the base portion 702d from over deformation caused by pressure from the oil-side O, and also slides on and seals the shaft 800.
Accordingly, the resin sealing member 703 is preferably made of a resin material having certain degree of bending resistance (or flexibility) in order to secure the shape thereof and the engagement with the shaft 800. Examples of such resin materials having specific flexibility (which means not so rigid), are fluoro polymers such as PTFE (Polytetrafluoroethylene) or the like.
Moreover, differing from the sealing lip or the like made of rubber which has sufficient elasticity, the resin sealing member 703 can not give a strong tension to all over the sealing periphery of the surface of the shaft. Oil leakage tends to occur due to the lack of tension in resin sealing member. In order to prevent oil leakage, grooves 704 having a pumping property are usually formed on the sealingly engaging surface of the resin sealing member 703.
The groove 704 has a structure to give the resin sealing member 703 a pumping function to pump oil back to oil-side O at the time there is relative rotational movement between the sealing device 700 and the shaft 800.
When the sealing device 700 is used in such a place where the shaft 800 is only driven in one rotational direction (not in reverse rotational direction) relative to the sealing device, the grooves 704 are preferably formed in a screw type manner, thereby providing the sealing device 700 with one way pumping effect. On the other hand, when the shaft 600 is driven in both normal and reverse rotational directions, a plurality of grooves 704 are preferably formed in a concentric circular manner, thereby exerting moderate pumping effect on the sealing device even in both normal and reverse rotations of the shaft 800. The distance or the gap between the shaft 800 and the housing 900 is effectively sealed by the sealing device mentioned above.
As is shown in FIGS. 14A and 14B (Japanese Patent Tokosho 60-56618), the resin sealing member 703 has been prepared to form the helical groove by using thread cutting means, on a surface 707 of an end portion of a resin tubular body 705, which has a predetermined inner and outer diameter made of resin material such as PTFE (Polytetrafluoroethylene or the like); and then cutting off the end portion by a cutting means 706 from the resin tubular body 705 to make a washer-like plain sealing member 703 with helical groove (as shown in FIG. 14A). Helical groove can be made by press forming processes as well as cutting processes. A pressing tool 800j, which has an approximately same outer diameter as that of the shaft 800 to be sealed, is inserted, by using a press machine or the like, into an inner hollow bore of the thus obtained washer-like plain sealing member 703, thereby bending a lip portion thereof at a predetermined angle and forming a sealing lip portion 703a which is designed to slide on and seal the shaft 800 (as shown in FIG. 14 B).
These conventional sealing members 703 have deficiencies as described below. There are some inefficiencies in the conventional manufacturing process such as groove forming process on the resin tubular body, cutting off process of the end portion, bending process to form sealing lip or the like.
Moreover, washer-like sealing members having large inner bore have a shortcoming in process because the productivity of the conventional sealing members 703 decreases with increases in wall thickness of the resin tubular body 705, and the material cost also becomes large with increases in wall thickness.
Further more, resin materials such as PTFE or the like have an extremely low in elastic elongation limit compared with elastomers usually having high elasticity, so the resin sealing member without bending process mentioned above, are prone to be inadvertently distorted or in some cases broken.
It is therefore an object of the present invention is to provide a sealing device having an excellent anti-abrasion property.
Another object of the invention is to provide a sealing device having an excellent sealing property in long use.
A still another object of the present invention is to provide a process of making a sealing device having an excellent anti-abrasion property.
A further object of the invention is to provide a process of making a sealing device having an excellent anti-abrasion property at low cost.
These objects of the present invention are achieved by a sealing device, comprising; a rigid annular casing provided with an elastic rubber like sealing lip disposed in an axial direction of the sealing device, and said sealing lip having a frustoconical air-side surface and having a frustoconical oil-side surface; and a harder helical portion disposed on said frustoconical air-side surface, the hardness of said harder helical portion being harder than the hardness of said sealing lip. The harder helical portion on the inner surface of the frustoconical air-side surface is formed by hardness variation making means which forms the harder portion on the surface of elastic rubber or rubber like materials.
Another objects of the present invention are achieved by providing a process for making a sealing device, comprising the steps of, preparing a foreproduct of said sealing device having a rigid annular casing, a molded elastomeric member bonded to said casing and a sealing lip defined by a frustoconical air-side surface and a frustoconical oil-side surface; radiating radiation ray on said frustoconical surface to form said harder helical portion.
The harder helical portion or harder portion can be obtained by inducing chemical reaction in rubber compositions. Chemical reactions can be induced by irradiation of radiation ray. The thus obtained harder portions have a pumping function to pump back oil or fluid to be sealed to oil or fluid side to give sealing devices excellent sealing properties. Said radiation ray is preferably an electron beam.
Another object of the present invention can be achieved by providing an additional sealing member comprising thermoplastic elastomer placed between a main rubber sealing lip and a rigid annular casing, said additional sealing member having a harder portion on its sealing surface. By providing such a harder portion by chemical process, a sealing device having high productivity and low cost as well as an excellent sealing property, can be obtained.
Further objects of the present invention can be achieved by providing a process for making a sealing device having the additional sealing member, comprising the steps of; preparing a sheet or a washer-like annular member made of a composition comprising thermoplastic elastomer;
radiating radiation ray on a predetermined surface of said sheet or washer-like annular member; and
molding said sealing device by placing, in a mold, a rigid annular casing, said radiated washer-like annular member and a rubber composition so as to set said annular member being placed between and held by said rigid annular casing and said rubber composition, said radiated washer-like annular member being bent in an axial direction thereof so as to make said radiated portion of said annular member slide on and seal the surface of said shaft.
The harder portion can be obtained by inducing chemical reaction in thermoplastic elastomer compositions. Chemical reactions can be induced by irradiation of radiation ray. The thus obtained harder portion has a pumping function to pump back oil or fluid to be sealed to oil or fluid side to give sealing devices excellent sealing properties.
Thermoplastic elastomer is used as a material of the additional sealing member in the sealing device. On the specific area of the surface of the additional sealing member, radiation ray is irradiated to change the properties of the surface of the sealing member.
The properties of the specific area of the surface of the sealing member, that is, the crosslinking condition or elasticity of the specific area, can be varied selectively and arbitrarily so that, by using this method, the changes in flexibility of the sealing lip portion can be carried out somewhat arbitrarily, or fluid or oil retention can also be achieved by forming minute convexo-concave configuration in the sealing region which contacts with the shaft to be sealed, or seal or drain of oil can also be achieved by designing the shape and configuration of the specific area.
There is also no need to use conventional mechanical machining process to obtain these properties in the sealing member, and there is no need to take such an additional process as bending the washer-like sealing member by inserting a pressing tool having the same diameter as that of the shaft, because of the thermoplastic elastomers having elasticity itself to bend easily with no damage thereof. Thereby the productivity can be greatly improved.
These features mentioned above derive from a cross-linking structure, and the degree of cross-linking can be adjusted by choosing both irradiation dose and irradiation energy of radiation ray.
Furthermore, the specific area of the sealing surface of the sealing member is preferably irradiated by radiation ray. When stress is applied to the sealing member, convexo-concave configuration is formed on the irradiated sealing surface of the sealing lip.
Sealing member is a washer-like annular member, which is preferably made of thermoplastic elastomer composition, and the inner diameter of the sealing member is bent in the axial direction thereof at the time the sealing device is mounted on the shaft, and the radially inner peripheral surface of the sealing member is used as a sealing which slide on and seal the shaft. Said radiation ray is preferably an electromagnetic wave. Said thermoplastic elastomer can preferably be selected from the group of fluorothermoplastic-based elastomers.
As for a process for manufacturing the sealing device, washer-like sealing member is preferably made of a composition comprising thermoplastic elastomer, and radiation ray is radiated on a specific region thereof to cause physical and chemical changes in the elastomer.